Re: aliased & packed?

[Stephen Leake <Stephen.Leake@gsfc.nasa.gov>]

Tom Moran wrote:
> 
> Clearly you can't do it.  I'd like to use pragma Pack for bits in a
> black/white bitmap array.  That's easy to manipulate.  But to actually
> display it I need to do a system call and pass the address.  If it
> wasn't packed, Image'unchecked_access would be appropriate.  But
> that won't work because Image would have to be aliased, and it can't
> be because it's packed. Must I drop 'Pack' and make it an array of
> bytes and do my own masking, shifting, etc?  What's the cleanest/most
> portable/best way to accomplish the task?

Since the system call wants the address, use 'address (converted to
Long_Integer or whatever is required). You have to do some conversion to
pass to a system call; converting from 'unchecked_access is no "cleaner"
than converting from 'address.

As for portability, there will be a different system call to display
bitmaps, so you'll have to change a lot more than the attribute!
-- 
- Stephe